1. Field
The present disclosure generally relates to systems and methods of removing a boundary layer of air from the incoming air flow of a jet engine.
2. Description of the Related Art
Turbojet propulsion systems are employed extensively in jet-powered aircraft. A tremendous amount of power can be extracted from a single, modern turbo-propulsion system. To generate this power with maximum efficiency, large quantities of propulsion-system air must be delivered to the engine face with minimum aerodynamic loss, turbulence, and flow distortion for a wide range of engine-operating conditions. As one example, a jet transport must inhale air efficiently in the near-static condition at the beginning of takeoff roll, in the relatively low-speed, high-power climb condition, and while cruising at high speed at high altitude. At all flight conditions, the propulsion-system air must be decelerated to a low-speed, high-pressure state at the engine compressor face. The detailed design of the air intake determines the efficiency with which the air is delivered to the propulsion system.
Fixed-geometry inlets are suitable for aircraft designed to operate at subsonic and low supersonic speeds. For flight at Mach numbers much beyond 1.6, however, variable-geometry features must be incorporated in the inlet if acceptably high inlet pressure recoveries together with low external drag are to be achieved. This complication is dictated by the physical laws governing the flow of air at supersonic speeds, and many supersonic aircraft have inlets with inlet features that vary automatically in a prescribed manner as the Mach number changes. In some aircraft, a compression ramp or cone that is disposed forward of the inlet aperture is moved forward or aft to maximize the inlet efficiency.
One of the sources of loss of efficiency is ingestion of the boundary-layer of the incoming air flow. Air flowing along a surface that is forward and proximate to the inlet aperture will develop a layer of air having a reduced velocity, and the mass of air delivered to the engine is reduced by the difference in the velocity of the boundary-layer air and the velocity of the free stream air. Previous approaches to removing this boundary layer from the air include the use of porous or perforated surfaces that either draw in the boundary layer air or inject additional air into the air stream to accelerate the boundary layer air. Some designs include diverter plates that deflect the boundary layer to the outside of the intake aperture. Some systems include chevrons or tabs that disrupt the boundary layer flow and mix the boundary layer air back into the free stream air. Other systems use fixed slots that draw in the boundary layer.